1. Field of the Invention
This invention relates to data transmission and in particular to a method and apparatus for transmitting digitally-coded data over power supply lines.
This manner of data transmission is especially useful for flight control networks in aircraft. The conventional use of triplex or quadruplex systems for flight control necessitates a large number of wires running from flight control computers to the various associated actuators. Combining the power bus and data bus together cuts down the amount of necessary wiring, thus reducing the weight and bulk of the network.
An object of the present invention is to provide a method and apparatus for enabling bi-directional data communication on a power supply line, which supply line may be AC or DC.
2. Description of the Prior Art
One known technique for achieving communication of data in this way (and shown in FIG. 1) uses a transformer T.sub.1 for coupling data from a transmitter 1 onto a power line 2. Data is extracted by a second transformer T.sub.2 and receiver 3 further down the power line. This arrangement functions satisfactorily if the supply current is steady. If, however, there is a surge, then the cores of the transformers could be driven into saturation. When this occurs, the transformers are no longer capable of transmitting or receiving the data signal. To increase the transformers' resistance to saturation, it is possible to incorporate an air gap between the core and transformer windings However this measure results in large and heavy devices which, in the aircraft control network application, is a disadvantage.